While reading some storage documentation this morning, I came across a chart which expressed disk sizes in a unit I’d never heard of before: MEBIBYTES.
“Huh? What the hell’s a mebibyte?” I wondered.
The explanation given in the text was only medium helpful:
“The numbers shown are in Mebibytes (MiBs). This unit of measure is
equivalent to 2 to the 20th power bytes. (MBs, in contrast, are 10 to the sixth power bytes.)”
Oh, ok. Thanks… 
A quick jump on the scientific calculator explains a bit further:
2^20 = 1,048,576
10^6 = 1,000,000
Anyone geek worth his salt knows that a kilobyte is not 1,000 bytes, but actually 1,024, hence a megabyte is acutally 1,024 x 1,024, which coincidentally equals 1,048,576. Ah ha – now we’re getting somewhere…!
A quick search on Google returned me to the ever reliable Wikipedia which solves my befuddlement with a few interesting nuggets of information.
Apparently, there is some ambiguity as to what megabyte actually means. According to Wikipedia:
“The megabyte (abbreviated as Mbyte or MB) is a multiple of the unit byte for digital information storage or transmission with three different values depending on context: 1048576 bytes (2^20) generally for computer memory; and one million bytes (10^6) generally for computer storage.”
To make matters worse, this ambiguity has cause screw ups on an global level in the past, most notably when the internationally recognised 1.44 MB floppy disk was incorrectly calculated on the basis of a “megabyte” being 1,024,000 bytes (or 1,024 x 1,000 as opposed to 1,024 x 1,024 or 1,000 x 1,000).
As a result, the IEEE Standards Committee have endorsed International Electrotechnical Commission’s definition of a Mebibyte (a combination of MEga and BInary) for situations where “use of a binary prefix makes sense”.
Phew – glad we got that cleared up then!
Do Sysadmins Dream Of Electric Sheep? 